Beta amyloid is certainly a central component in Alzheimer's pathology. No one refutes that it is toxic to brain cells and that an accumulation of amyloid plaques is a hallmark indicator of Alzheimer's disease.

The amyloid hypothesis suggests heavy amyloid deposition in the brain is the underlying cause of this disease and we have discussed it here on many occasions (read past posts on the amyloid hypothesis here).

Having said that, there is no consensus and no well-validated explanation of why beta amyloid accumulates in some brains and not others. Nor is there a definitive understanding of why some people have lots of amyloid deposition but remain cognitively sharp.

Because an increased production of beta amyloid is a known reaction to head trauma and stroke, some have hypothesized that it plays a neuro-protective role and its presence is an indication of the brain attempting to repair itself from some other harm. Accordingly, beta amyloid could be viewed as part of a solution to some other problem.

Scientists at Massachusetts General’s Institute for Neurodegenerative Disease suggest that the other problem might be microbial infection. Their research, published in the journal PLos One, showed that brain tissue with lots of beta amyloid taken from Alzheimer's patients inhibited growth of several infectious organisms whereas brain tissue taken from healthy adults did not. This suggests that increased production of beta amyloid might be a natural defense mechanism when certain infections are present in the central nervous system.

If such an "infection hypothesis" is confirmed as the underlying cause of Alzheimer's, it would support the notion that amyloid toxicity is what degenerates the brain in Alzheimer's patients but would suggest a different treatment approach. That is, rather than removing the amyloid, a better approach would be to remove the infection that is stimulating amyloid production.

At that point, the challenge would be to find treatments that can cross the blood/brain barrier and fight infection in the brain.